Corals that glow and display a wide range of fluorescent colors have been discovered in deep-water reefs of the Red Sea, according to researchers.
Corals living more than 150 feet below the surface glow with bright fluorescent colors including greens, reds and yellows — a surprise to the scientists from Israel and the United Kingdom, as shallow-water corals in the same region only show green monochromatic fluorescent pigments.
"These fluorescent pigments are proteins," explained Jörg Wiedenmann, a professor of biological oceanography at the UK's University of Southampton. "When they are illuminated with blue or ultraviolet light, they give back light of longer wavelengths, such as reds or greens."
In shallow water, the colors contained in corals act as a sort of natural sunscreen, but sunlight doesn't penetrate water to the depths of 150 feet below the surface. This raised the question of why the corals create pigments that require a lot of energy to produce.
These pigments may aid the corals in harvesting the small amount of energy by photosynthesis from the little light that does reach them. They may then feed it to the symbiotic algae that provide a food source for the corals, the researchers suggest in their study published in the journal PLoS One. But that's just one possibility.
"The underlying mechanism is not understood," said Wiedenmann, who heads his university's Coral Reef Laboratory. "Hopefully our future work can reveal their function."
Even if poorly understood, some of the coral pigments could be a source for imaging tools for medical applications, the researchers suggest.
"Their optical properties potentially make them important tools for biomedical imaging applications, as their fluorescent glow can be used to highlight living cells or cellular structures of interest under the microscope," Weidenmann explained. "They could also be applied to track cancer cells or as tools to screen for new drugs."
Corals on what are known as mesophotic reefs have been little studied. That's because they're below the depth limits of normal scuba diving equipment and techniques, according to Gal Eyal, a doctoral candidate at the Interuniversity Institute for Marine Sciences in Israel.
"Advances in technical diving have enabled us to explore coral communities from these deeper waters," Eyal said.
The researchers say they are continuing to explore what other biological functions the corals' fluorescent pigments may provide.